UIResponder

UIResponder

An abstract interface for responding to and handling events.

Users manipulate their iOS devices in a number of ways, such as touching the screen or shaking the device. iOS interprets when and how a user is manipulating the hardware and passes this information to your app.

Overview

Responder objects—that is, instances of UIResponder—constitute the event-handling backbone of a UIKit app. Many key objects are also responders, including the UIApplicationobject, UIViewController objects, and all UIView objects (which includes UIWindow). As events occur, UIKit dispatches them to your app’s responder objects for handling.

There are several kinds of events, which includes

touch events

motion events

remote-control events (because it can originate from an external accessory)

In addition to handling events, UIKit responders also manage the forwarding of unhandled events to other parts of your app. If a given responder does not handle an event, it forwards that event to the next event in the responder chain. UIKit manages the responder chain dynamically, using predefined rules to determine which object should be next to receive an event. For example, a view forwards events to its superview, and the root view of a hierarchy forwards events to its view controller.

Responders process UIEvent objects but can also accept custom input through an input view. The system’s keyboard is the most obvious example of an input view. When the user taps a UITextField and UITextView object onscreen, the view becomes the first responder and displays its input view, which is the system keyboard. Similarly, you can create custom input views and display them when other responders become active. To associate a custom input view with a responder, assign that view to the inputView property of the responder.